.8x^2=200

Solution for .8x^2=200 equation:

.8x^2=200

We move all terms to the left:

.8x^2-(200)=0

a = .8; b = 0; c = -200;
Δ = b2-4ac
Δ = 02-4·.8·(-200)
Δ = 640
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{640}=\sqrt{64*10}=\sqrt{64}*\sqrt{10}=8\sqrt{10}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-8\sqrt{10}}{2*.8}=\frac{0-8\sqrt{10}}{1.6}
=-\frac{8\sqrt{10}}{1.6}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+8\sqrt{10}}{2*.8}=\frac{0+8\sqrt{10}}{1.6}
=\frac{8\sqrt{10}}{1.6}
$